package 第8周_二分搜索树.集合与映射.Map;

public class BSTMap<K extends Comparable<K> , V> implements Map<K, V> {

    private class Node{
        public K key;
        public V value;
        public Node left, right;

        public Node(K key, V value){
            this.key = key;
            this.value = value;
            left = null;
            right = null;
        }
    }

    private Node root;
    private int size;

    public BSTMap(){
        root = null;
        size = 0;
    }

    @Override
    public void add(K key, V value) {
        root = add(root, key, value);
    }

    private Node add(Node node, K key, V value){
        if (node == null){
            size++;
            return new Node(key, value);
        }

        if (key.compareTo(node.key) < 0){
            node.left = add(node.left, key, value);
        }else if (key.compareTo(node.key) > 0){
            node.right = add(node.right, key, value);
        }else {
            node.value = value;
        }
        return node;
    }

    /**
     * 返回以node为根节点的二分搜素树中， key所在的节点
     * @param node
     * @param key
     * @return
     */
    private Node getNode(Node node, K key){
        if (node == null){
            return null;
        }

        if (key.compareTo(node.key) == 0){
            return node;
        }else if (key.compareTo(node.key) < 0){
            return getNode(node.left, key);
        }else {
            return getNode(node.right, key);
        }
    }


    /**
     * 返回以node为根的二分搜索树的最小值所在的节点
     * @param node
     * @return
     */
    private Node minimum(Node node){
        if (node.left == null){
            return node;
        }
        return minimum(node.left);
    }

    /**
     * 删除掉以node为根的二分搜索树中的最小的节点
     * 返回删除节点后新的二分搜索树的根
     * @param node
     * @return
     */
    private Node removeMin(Node node){

        if (node.left == null){
            Node rightNode = node.right;
            node.right = null;
            size--;
            return rightNode;
        }

        node.left = removeMin(node.left);
        return node;
    }


    @Override
    public V remove(K key) {
        Node node = getNode(root, key);
        if (node != null){
            root = remove(root, key);
            return node.value;
        }

        return null;
    }

    /**
     * 删除掉以node为根的二分搜索树中键为key的节点，递归算法
     * 返回删除节点后新的二分搜索树的根
     * @param node
     * @param e
     * @return
     */
    private Node remove(Node node, K key){
        if (node == null){
            return null;
        }
        if (key.compareTo(node.key) < 0){
            node.left = remove(node.left, key);
            return node;
        }
        else if (key.compareTo(node.key) > 0){
            node.right = remove(node.right, key);
            return node;
        }
        else {
            //待删除的节点左子树为空的情况
            if (node.left == null){
                Node rightNode = node.right;
                node.right = null;
                size--;
                return rightNode;
            }
            //待删除的节点为右子树的情况
            if (node.right == null){
                Node leftNode = node.left;
                node.left = null;
                size--;
                return leftNode;
            }

            //待删除的节点左右子树皆不为空
            //找到比待删除节点大的最小节点，即待删除节点右子树的最小节点
            //用这个节点顶替待删除节点的位置
            Node successor = minimum(node.right);
            successor.right = removeMin(node.right);
            successor.left = node.left;
            node.left = node.right = null;
            return successor;
        }
    }

    @Override
    public boolean contains(K key) {
        return getNode(root, key) != null;
    }

    @Override
    public V get(K key) {
        Node node = getNode(root, key);
        if (node == null){
            return null;
        }
        return node.value;
    }

    @Override
    public void set(K key, V value) {
        Node node = getNode(root, key);
        if (node == null){
            throw new IllegalArgumentException("你输入的key不存在！");
        }
        node.value = value;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }
}
